Cryogen temperature indicator

ABSTRACT

A diode, which will vary its voltage in response to a variance in temperature, is housed in a heat sink. The heat sink is placed into a cryogenic material whose temperature is to be measured. The voltage across the diode is indirectly measured so as to give an indication of the temperature of the cryogen.

United States Patent 1191 11] 3,780,585 Milo Dec. 25, 1973 [54] CRYOGENTEMPERATURE INDICATOR 3,603,150 9/1971 Kurtin 73/362 SC [75] Inventor:William C. Milo, Anaheim, Calif. OTHER PUBLICATIONS [73] Assignee: TheUnited States of America as (80201-0046) Huen F Divid? represented bythe Secretary of the Temperature Thermometer. In Rev1e;/ of Sc1ent1f1cArmy, Washington DC Instruments. Vol. 41, No. 9. pp. 1368- (Sept. 1970).(L 7250-0006). Regulador de Temperature. In [22] plied: 12, 1972 RevistaTelegrafica Electronica, Oct., 197i: p. 590. 21 Appl. No.2 217,356 4159-Primary Examiner-Donald O. Woodie] 52 vs. C] 73/362 sc, 307/310, 330/23Assistant Examiner prederick Shoo 51 Int. Cl. GOlk 7/24, GOlk 1/20,I-IO3f 1/30 A,mmey charles Wright et [58] Field of Search 73/362 SC;307/310;

- 330/23 57 ABSTRACT [561 @3312 iiilii l illi iifiollifi fn I fiZZiZiSEin: UNITED STATES PATENTS heat sink is placed into a cryogenic materialwhose 3,260,l l5 7/1966 Logan 73/362 SC temperature is to be measuredThe oltage across the $223232 2; E???" diode is indirectly measured soas to give an indication 1g ner 3,473,385 lO/l969 KilClll Komatsubara73/362 A of the temperature of the cryogen' 3,57l,735 3/1971 Ducamus330/23 X 1 Claim, 1 Drawing Figure 1 CRYOGEN TEMPERATURE INDICATORBACKGROUND OF THE INVENTION This invention is related to the field oftemperature measurement. More particularly this invention is related tothe field of cryogenic temperature measurements. Prior art devices formeasuring cryogenic temperatures required a high cost, and the packagingwas bulky. None of prior art devices lent itself to be packaged in amicrocircuit or in a small meter panel.

SUMMARY OF THE INVENTION This invention utilizes the voltage changeacross a diode due to a change in temperature. The diode is located in aheat sink which is subjected to the temperature desired to be measured(such as the temperature of a cryogen). The change in the temperature ofthe heat sink will cause the temperature of the diode to vary with it. Asource of d-c voltage is regulated to a constant value and suppliescurrent through a resistor to the diode. As the voltage across the diodevaries due to temperature changes, the voltage across the resistor willalso vary. An amplifier is connected across the resistor so as to sensechange in the voltage of the resistor. This amplifier feeds a metercircuit which is calibrated in degrees kelvin so as to directly read thetemperature of the cryogen. The amplifier is made up of two gangedtransistors. Two seriestransistors are provided in the diode circuit forambient temperature compensation.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a schematicshowing of the preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A diode 1, such as a silicondiode or any of the diodes which will vary their voltage in response totemperature, is housed in a heat sink 3 which is shown partially cutaway. Heat sink 3 can take any of the known forms, such as a probe form.The diode 1 will vary at a value of 2.5 millivolts per degree kelvin orcentigrade change. The preferred embodiment illustrated has a range of100 kelvin. The location in the temperature scale of the range is set bythe trim pot 5 in correspondence with resistor 6. A common range formeasuring cryogenic materials is in the range of 177 kelvin to 77kelvin. Meter 8 may be any of the well known meters, such as a phaostronprestige II, 1 ma movement meter. Meter 8 can be calibrated by placingthe diode 1 in boiling liquid nitrogen and varying the trim pot until 77kelvin is full scale.

A d-c voltage source 10 is regulated to a constant value by voltageregulator 11. Voltage regulator 11 is made up resistor 13, zenor diode15 and transistor 16. Voltage regulator is well known in the art andwill provide an output at the emitter of transistor 16 which is aconstant voltage, as long as d-c voltage source 10 is within a certainvoltage range. A large resistor 18 is connected in series withtransistors 20 and 21. Voltage source 10 will feed current to diode l byway of regulator l1, resistor 18, andtransistors 20 and 21. As thevoltage across diode 1 changes due to change in temperature, the currentflow through diode 1 will change; therefore, causing the voltage acrossresistor 18 to vary in accordance with the temperature variance. Anamplifier circuit 25 is provided to sense the voltage change acrossresistor 18. Amplifier 25 consist of transistors 27 and 28 which areganged together by way of resistors 29, 30 and 31. The output amplifier25 is fed to meter 8 by way of filter 33; therefore meter 8 senses thevoltage across amplifier 25 which in turn senses the voltage across 18which in turn is proportional to the voltage across diode 1. From allthis, it can be seen that meter 8 will sense the temperature of heatsink 3 which is subjected to the temperature desired to be measured.With proper calibration meter 8 will therefore read the temperaturedesired.

Transistors 27 and 28 will change their impedance due to ambienttemperature changes. In order to compensate for this transistors 20 and21 are provided in the diode side of the circuit and subjected to thesame ambient temperature so as to balance any impedance changes intransistors 27 and 28 by corresponding change in impedance bytransistors 20 and 21. Transistors 20 and 21 have their collectorsconnected directly to their bases so as to keep transistor 20 and 21 inan on condition. All of the resistors and the trim pot of the system aretemperature stable components.

I claim:

1. A temperature measuring circuit comprising a source of dc voltages; aregulator connected across said source of dc voltages so as to regulateits output to a constant voltage; a resistor; first and secondtransistors each having its base connected to its own collector; asilicon diode; said source of dc voltages, resistor, first and secondtransistors, and said diode being connected in a series circuit; heatsink means inclosing said silicon diode; said heat sink and diode beingplaced in the vicinity of the temperature to be measured; a thirdtransistor having its input connected across said resistor means; afourth transistor having an input connected to the output of said thirdtransistor whereby said transistors are ganged together; measuring meansconnected to the output of said fourth transistor so as to measure thetemperature; and said first and second transistors compensating forchanges in the operation of said third and fourth transistors due totemperature.

1. A temperature measuring circuit comprising a source of dc voltages; aregulator connected across said source of dc voltages so as to regulateits output to a constant voltage; a resistor; first and secondtransistors each having its base connected to its own collector; asilicon diode; said source of dc voltages, resistor, first and secondtransistors, and said diode being connected in a series circuit; heatsink means inclosing said silicon diode; said heat sink and diode beingplaced in the vicinity of the temperature to be measured; a thirdtransistor having its input connected across said resistor means; afourth transistor having an input connected to the output of said thirdtransistor whereby said transistors are ganged together; measuring meansconnected to the output of said fourth transistor so as to measure thetemperature; and said first and second transistors compensating forchanges in the operation of said third and fourth transistors due totemperature.